1. Field of the Invention
The invention relates to control linkages for hydrostatic transmissions, and the neutral return mechanisms such linkages provide.
2. Description of the Related Art
It is known to provide conventional lawn tractors with hydrostatic transmissions. These transmissions typically have an input means or input shaft which extends outwardly from the transmission housing. When this shaft is pivoted in a first direction from a neutral position the transmission propels the tractor in a forward direction, and when the input shaft is pivoted in the other direction the transmission propels the tractor in reverse. The degree to which the input means is pivoted, either in the forward or reverse direction, controls the velocity of the tractor. An operator control such as a foot pedal or hand lever is typically coupled to the end of a linkage which extends between the shaft and the operator station. The operator control is thereby shiftable by the operator for controlling the direction and speed of the vehicle.
Some such vehicles having hydrostatic transmissions provide mechanisms which automatically return the shaft to its neutral position in situations such as when the operator removes his foot from an accelerator pedal or when the operator applies a vehicle brake. By returning the shaft to its neutral position, the hydrostatic transmission is allowed to free-wheel instead of continuing to drive or propel the vehicle when the operator lifts his foot from the accelerator or when the operator applies the brake.
Typical neutral return mechanisms include a plate having a V-shaped cam surface formed therein. Typically the plate is operatively coupled for pivotal motion with the transmission input shaft. A cam follower is provided which is selectively urged against the V-shaped cam surface for returning the pivoted plate and input shaft to their neutral position. As the cam follower presses against one of the legs of the V-shaped cam surface the plate will pivot back to its neutral position, and the cam follower will come to rest near the base of the V where the two legs meet. Due to the V shape of the cam the roller can make proper contact with the cam when the cam is pivoted in either the forward or the reverse directions. The roller is therefore capable of returning the transmission to neutral regardless of the vehicle's direction of travel.
Conventional neutral returns typically include a generally large number of parts and thereby undesirably add to the cost of manufacturing the vehicle. It would be desirable to provide a vehicle having a hydraulic transmission with a neutral return feature composed of relatively few parts and which is relatively inexpensive to manufacture. Some conventional neutral return mechanisms require a large amount of force be applied to the plate by the cam follower in order for the plate to pivot back to its neutral position. It would therefore be desirable to provide a neutral return mechanism which returns the plate to its neutral position without requiring a large force being applied by the cam follower. Ease of operation and operator feel would thereby be enhanced.